EFFECT OF CHAR PREPARATION TEMPERATURE ON THE EVOLUTION OF NITROGEN-CONTAINING SPECIES DURING CHAR OXIDATION AT FLUIDIZED BED CONDITIONS

摘要

This study considered the effect of pyrolysis temperature on the conversion of char-N to N_2O, NO and HCN in fluidized bed combustion. The experiments conducted in a laboratory scale batch fluidized bed reactor with an anthracite coal showed that an increase in the pyrolysis temperature produced a reduction of the conversion of char-N to N_2O and HCN, while the conversion to NO increased. Different explanations of this behavior were explored. The lower hydrogen content of the chars produced at higher temperatures and their lower reactivity may account for a reduction of the formation of HCN, as an intermediate for N_2O evolution. It is also possible that the lower char reactivity observed for chars produced at higher pyrolysis temperatures may affect the reactions occurring in the boundary layer. In particular, chars of lower reactivity may react at lower particle temperature and under higher transient oxygen concentrations. The effect of temperature and equivalence ratio on the oxidation of HCN is studied by a simplified representation of char combustion. The results suggest that at conditions similar to those of this study, reduction of the equivalence ratio may explain observed variations in product distribution as pyrolysis temperature increases.